A drain pump is a key component used in a washing machine and a dishwasher. Operation of the drain pump has three working states, i.e. a startup state, water draining state, and mixed air and water draining state. In the mixed air and water draining state, since most water has been drained out, only a small amount of residual water is left which is mixed with air to form a mixed fluid. As a result, the drain pump generates large noises.